NASA scientists found drug-resistant strains of bacteria in the ISS toilets, but say they pose no threat to the astronauts—for now.

Drug-resistant bacteria—germs that have adapted immunities to antibiotic treatments—have found their way to the International Space Station, according to a new study.

Led by Nitin Singh, a microbiologist at NASA’s Jet Propulsion Laboratory, the study, published in BMC Microbiology, examined five strains of Enterobacter bacteria from samples collected in 2015 from the toilets and exercise equipment onboard the ISS.

Enterobacter is a common and mostly harmless bacterial family, but drug-resistant strains of the organism have been flagged in hospitals. A 2015 outbreak in a Tanzanian neonatal unit, for instance, caused blood infections in newborn babies.

Singh and his colleagues wanted to assess the virulence of the Enterobacter strains on the ISS compared to antimicrobial-resistant pathogens on Earth. To do this, the team mapped the genomes of the space strains and compared them to the roughly 1,300 known Enterobacter genomes.

Their analysis revealed that the five strains were most genetically similar to Enterobacter bugandensis, the same drug-resistant species responsible for the Tanzania outbreak.

The finding corroborates a Nature paper from January that suggested E. bugandensis might be present on the space station. Singh’s team expanded beyond that research by evaluating the genetic virulence of the strains and their potential to infect the astronauts.

The upshot is that these space bugs do not pose any immediate threat to ISS crews because they are genetically distinct from the most infectious forms of E. bugandensis. But there is enough overlap between the ISS germs and their pathogenic Earth cousins to warrant careful attention to the microbiome going forward.

“These species potentially pose important health considerations for future missions,” Singh said in a statement. “However, it is important to understand that the strains found on the ISS were not virulent, which means they are not an active threat to human health, but something to be monitored."

Bacterial strains can adapt rapidly to new habitats, so the relatively benign bugs on the ISS today may not be harmless forever. It’s difficult to keep pace with drug-resistant bacteria, so the CDC suggests focusing on preventative measures, like isolating infected patients and paying careful attention to antibiotic prescriptions.

Of course, such guidelines are a lot more difficult to impose on patients living 220 miles above Earth, which is why ISS researchers will have to keep close tabs on the station’s bacterial community.